GPT-5.6 Document Translation

Sol, Terra and Luna — measured, not marketed

The previous-generation GPT-5.5 is included as a baseline, because Sol carries an identical list price and the comparison is the one most people actually need.

Which tier should you actually pay for?

1. You need the best translation you can get

   Sol

   It reached a perfect score in five of the eight scenarios. It also costs the same list price as GPT-5.5 while scoring 0.16 higher and spending less per call, because it writes fewer output tokens to say the same thing.

2. Latency is what you are optimising

   Terra

   At a median 3,598 ms it was the fastest of all seven models we tested, and it still scores 4.38 — comfortably above the open-weight alternatives.

3. Cost is what you are optimising

   Terra, for now

   Luna has the lowest cost per quality point of the family, but it is not offered on Belin Doc yet. Among the tiers you can select today, Terra is the cheaper one.

How GPT-5.6 places against everything else we tested

The top three finish within 0.03 points of each other — inside judge noise. What separates them is price: Sol reaches that level at one of the two lowest costs per quality point in the field, while Gemini 3.1 Pro costs about 3.4 times more per point.

Where Sol earns its score

Judges scored every translation on five dimensions, 1 to 5. These are Sol's medians across all eight scenarios.

Faithfulness

4.8

Nothing added, nothing quietly dropped — the hard requirement for contracts and research papers.

Fluency

4.8

Reads as if it were written in the target language, not decoded from the source.

Terminology

4.8

A defined term on page 3 is still the same term on page 80, across the whole document.

Style

4.7

Register survives the crossing: legalese stays legal, literary prose stays literary.

Formatting

4.5

Tables, code identifiers and Markdown structure come through intact.

Translate with GPT-5.6 in three steps

1. 01

   Upload your document

   Drop in a PDF, Word, PowerPoint, Excel or EPUB file — whole books included.

2. 02

   Pick Sol or Terra

   Choose the GPT-5.6 tier that matches your priority, then set the target language.

3. 03

   Download the translation

   Layout, tables and terminology come back preserved, in the original file format.

GPT-5.6 document translation FAQ

What people ask before choosing a tier.

What is the difference between GPT-5.6 Sol, Terra and Luna?

They are three capability tiers of the same generation, not three generations. Sol has the highest reasoning ceiling and the highest price ($5 / $30 per 1M input / output tokens). Terra is the balanced tier ($2.50 / $15). Luna is the lightweight, cheapest tier ($1 / $6). In our benchmark Sol averaged 4.70, Terra 4.38 and Luna 4.34.

Which GPT-5.6 tier is best for document translation?

Sol, for anything where quality matters — it scored a perfect 5.00 in five of our eight document scenarios. Choose Terra when latency matters: at a median 3,598 ms it was the fastest of the seven models we tested, and it still scores 4.38.

Can I use GPT-5.6 Luna on Belin Doc?

Not currently. Belin Doc offers GPT-5.6 Sol and GPT-5.6 Terra. Luna was included in our benchmark for completeness, and we publish its results so the family comparison is honest, but it is not selectable as a translation model today.

Is GPT-5.6 better than GPT-5.5 for translation?

Sol is: it scores 4.70 against 4.54 at the same list price, and it costs less per call because it produces fewer output tokens. Terra and Luna score below GPT-5.5 on overall quality, but cost roughly a half and a third as much per call respectively — which is the trade they exist to offer.

How were these scores measured?

Seven models translated eight document scenarios — academic, legal, technical, literary, manga dialogue, Markdown tables, long-document terminology and more — three times each, for 168 translations. Candidate translations were anonymised and reshuffled each round, then scored 1 to 5 by two judges, GPT-5.4 and Claude Opus 4.7. Neither judge was a contestant, so no model graded itself. Every raw translation and judge score is archived in full, and the numbers reported here come straight from that archive.

How much does GPT-5.6 translation cost?

Measured on real documents rather than list price: Sol averaged $0.00360 per call and Terra $0.00161. Divided by the quality score they achieve, that is $0.00077 and $0.00037 per quality point. On Belin Doc you can start translating for free; larger documents and premium models may use credits depending on your plan.

Which file formats and languages are supported?

PDF, Word (DOCX), PowerPoint (PPTX), Excel, EPUB and more, with the original layout, tables and formatting preserved. Belin Doc supports translation across 100+ languages.

Is GPT-5.6 document translation free?

You can start translating for free. Free monthly pages are included on every account, and larger documents or premium models may draw on credits depending on your plan.

Sources

Every number on this page is traceable. The scores and latency come from measurements we ran ourselves; the prices are taken straight from the vendor’s official pricing page. Nothing here is quoted from a launch announcement.

Only the last two rows link out: the pricing row goes to OpenAI’s official pricing page, and the review carries the full per-scenario breakdown. The first two rows name the raw measurement artifacts these numbers were computed from.

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